1. Field of the Invention
The present invention is directed to a timber surface improving treatment process, and more particularly to a plasma process of improving surface properties of the timber by exposure to a plasma mixture at near atmospheric pressure.
2. Description of the Prior Art
For many years there have been constant demands for improving surface properties of a timber. Particularly, surface wetness is of a major concern in that a hydrophilic property is required for giving improved adhesiveness and printability to the timber while a hydrophobic property is required for giving water-repellant property to the timber. To this end, surface coatings have been generally employed in order to modify the surface properties of the timber. However, such coatings will certainly impair woodenness, and further pose another problem as to durability and weatherability in that the coating might be flaked off during an extended life of use in outdoors or in water-exposure conditions.
In the meanwhile, there have been known plasma processes for improving surface properties of an article such as plastics, silicon, and magnetic data storage media, as disclosed in U.S. Pat. Nos. 4,749,440 and 4,863,809. However, because such plasma process requires a high level of vacuum to generate a plasma by glow-discharging, its application to surface improvement of timber inherently containing water or moisture is practically impossible in that a stable plasma could not be obtained in the presence of the vapor of the moisture appearing at such high level of vacuum. On the other hand, some recent developments enable a plasma surface treatment at near atmospheric pressures, as proposed in Japanese non-examined early publication (KOKAI) Nos. 1-306569 and 2-15171 which teach the generation of a plasma mixture of an inert gas and a reactive monomer gas by glow-discharging at near atmospheric pressure to deposit a polymerized film on the surface of an article such as ceramics, glasses, plastics, and metals. With the advent of the plasma process at near atmospheric pressures, it is contemplated to apply the plasma process to timber for improving surface properties thereof. In anticipation that timber could be improved over a large surface area by such plasma process, attempts have been made by the inventors. Nevertheless, only insufficient surface improvement is obtained with this plasma process contrary to what would be expected, although the plasma is successfully generated.